This invention relates to a power source for gas discharge lamps and other loads operated at high frequency, typically power sources for driving fluorescent tube lamps from a dc supply or a standard 50 Hertz or 60 Hertz ac supply. Power sources of this general type are shown in U.S. Pat. Nos. 3,396,307; 3,889,153; 4,005,335; 4,017,785; and 4,127,797.
The present invention is directed to an improvement on that shown in U.S. Pat. No. 4,127,797, particularly the circuit of FIG. 7.
Efficiency of operation is a factor in most lighting systems, and it has been determined that better efficiency is obtained by operating the lamps or other load at a substantially constant power with changes in supply voltage and other parameters such as temperature, variations in load with change in temperature, variations in characteristics of circuit elements with temperature and time, and the like.
Accordingly it is an object of the present invention to provide a new and improved power source utilizing current feedback to produce substantially constant power output.
A problem is encountered in power sources utilizing current feedback such as in the aforesaid U.S. Pat. No. 4,127,797, under open circuit conditions when the output circuit wiring capacitance across the lamps is sufficient to maintain oscillation. When a lamp goes out or when there is some other malfunction in the output circuitry, there is an open circuit in the secondary side of the inverter transformer which can result in undesirably high voltages in the circuitry at the primary side of the transformer, and sometimes in permanent damage to circuit components.
It is another object of the present invention to provide a new and improved power source utilizing an inverter with current feedback and supplementary open circuit protection. Other objects, advantages, features and results will more fully appear in the course of the following description.
High power factor is an important factor in operation of lighting systems as well as other electrical systems from an AC supply. In operating a DC load from a rectified AC supply, a filter of some nature is utilized and better filtering is normally achieved at increased cost and size of the filter circuit.
It is another object of the present invention to provide a new and improved power source utilizing current feedback and operated in conjunction with a new and improved filter to obtain an increase in power factor.